I need help designing my sub box. Decided to go with bandpass and would like to have it play 20-80 (if possible...?). The subs are 2 old school JBL 1200GTi. Here are the specs: Vas = 2.4 cu.ft. Fs = 30 Hz Qms = 5.77 Qes = 0.45 Qts = 0.42 My box has to be about 39 inches wide, 14 inches deep, 16 inches tall with small extensions on the sides of the box to go over rear wheel wells (approx. 3in wide, 8in high and 14in deep (measuring from the top of the box). So the total net volume would be about 5.1 cu ft (using 3/4 MDF). Could someone tell me what the size of rear chambers and front chambers for each woofer would be and the size of the ports? I would like to do the single reflex bandpass (venting just the front chamber(s). Please help me...
I have some of those old JBLGTis at home. I don't think we can do much for the enclosure with that space, cause I believe sealed enclosure size was right at 5 feet. I'll drop a model tonight for you, but as I say...I think it is a lost cause
I tried modeling up an enclosure for you, and man, to get the response you want, you're gonna need a box the size of your car. :lol: :lol: Yeah, but as seth said, you are really gonna need a lot of space for a bandpass for those subs.
According to the factory manual, the sealed box is 1.35 cu ft, ported 2.5, bandpass 1.85 cu ft per driver... Then again, I found someone's info on the web that the factory specs are wrong and the Fs should 30 (not 37) and Qts 0.42 vs. 0.47... big difference when designing the box... I ran WINisd and the freq response shows very sharp peak betw. 35-40 Hz (way too high for my taste and very steep roll off around 60)... that was using 1.8 rear and 1.2 front volumes... what is up with this? I do not understand the plot either because it does not say if this is in car response or out of car (makes a big difference too, I think?) I don't understand the port entry in the program either... is single as a single per driver or per box? I cannot see doing the BP using just one port... LOL... I am having helluva time trying to sort things out... No wonder nobody is using BP... If I went with the 6th order, how do you size ports then? And I assume this design would be even easier to screw up... The BP is really easy to live in my Pathfinder since I can load stuff behind the box not worrying about damaging the drivers or choking them... gosh, there must be a way to do this... :unsure:
yeah, I finally downloaded the WINisd and tried to run it... The freq response comes up pretty high, narrow banded and very steep curve... Plenty loud though with 750 watts of power to the drivers...
you can search online for results of other people's tests (I was lucky with mine) or you can determine the specs yourself (there are tutorials available online how to do that) if you think you can do that (I do not trust my ability, LOL)... And the factory determined specs are often wrong but if this is the only thing you can go by, then it is still better than nothing...
